I just responded to your pm asking the exact same question but I'll put it up here so everyone else can see too. To start with on the seal we use a Teflon seal that sits under the cap. When the cap is tightened this compresses against the top of the bottle and forms a liquid tight seal. Now regarding the darkness of the fuel, this is simply out anti-oxidant (rust inhibitor) whis is photo-reactive.
It's a little unusual but it darkens with exposure to uv radiation (just like film does) but just like it says on the label if you read it, this has absolutely no affect on the perfomance or stability of the fuel at all. As I mentioned this is a strange effect but out of all of the testing we have done it is the best anti-oxidant that we have been able to find! The net effect of this though will be that say you have a bottle of fuel sitting around for a while it will go from clear to slightly yellow'ish to something close to the color of apple juice to dark brown then to something close to black lol! It's really kinda interesting to see and again it is solely a result of the photo-reactivity of our anti-oxidant which actualy only represents about 4PPM (4 parts per million) of the total volume of fuel, so were talking a really really minute part of the fuel.
Again though this in no way affects the performance or protective capabilities of the fuel. Kortz and Bradley were running some fuel in LA earlier in the season that Kortz had in his garage for nearly 2 years and was completely black in color. Worked just fine and everyone thought it looked kinda cool lol!
Just be aware that when you switch to our fuel you are prbably going to have to significantly lean out your engine. Thus will result in a significant increase in run time. The fuel also offers significant increases in performance, frankly it is a true racing fuel that still offers exceptional protection because of the lubricant quality and the addatives package that we use, one of which is that anti-oxidant that changes colors lol! Hope this helps explainthings a bit.
Regards,
Ron